Neurophysiological Apparatus and Procedures

ABSTRACT

Neurophysiological instruments and techniques are improved through various enhancements. Stimulation of an instrument is possible while it is advancing into the spine or elsewhere, alerting the surgeon to the first sign the instrument or device (screw) may be too near a nerve. A directional probe helps surgeons determine the location of the hole in the pedicle. Electrically insulating sleeves prevent shunting into the soft tissues. According to a different improvement, the same probe to be used to stimulate different devices, such as screws and wires. Electrical impulses may be recorded from non-muscle regions of the body, including the spine and other portions of the central nervous system as opposed to just the extremities.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/798,297 filed Oct. 30, 2017, currently pending, which is acontinuation of U.S. patent application Ser. No. 14/855,156 filed Sep.15, 2015, now U.S. Pat. No. 9,801,668, which is a continuation of U.S.patent application Ser. No. 12/359,269 filed Jan. 23, 2009, now U.S.Pat. No. 9,131,947, which is a continuation of U.S. patent applicationSer. No. 10/842,192 filed May 10, 2004, abandoned, which claims thebenefit under 35 U.S.C. § 119(e) to U.S. Provisional Patent ApplicationNo. 60/468,981, filed May 8, 2003, and to U.S. Provisional PatentApplication No. 60/530,427, filed Dec. 17, 2003, the entire contents ofwhich are each hereby expressly incorporated by reference into thisdisclosure as if set forth fully herein.

FIELD OF THE INVENTION

This invention relates to neurophysiological techniques and, inparticular, to improved instruments and procedures to ensure accurate,real-time, temporary or permanent placement of surgically implanteddevices.

BACKGROUND OF THE INVENTION

Pedicle instrumentation is often used to facilitate spinal fusion.Pedicle screws extend through the pedicles of vertebrae and into thebody of the vertebrae. The screws are connected by rods or plates toeliminate motion between the vertebrae that are fused together.

Misplaced pedicle screws can injury the nerves and blood vessels thatsurround the vertebrae. Numerous techniques are used to help surgeonsguide screws into the pedicles of the vertebrae. For example, surgeonsoften use x-rays including fluoroscopy to confirm the position ofpedicle screws.

Nerve compression by pedicle screws can also be determined throughelectrical stimulation of the pedicle screws. Prior-art techniquesinvolve recording electrical impulses in the legs or arms afterelectrical stimulation of the pedicles. High conductivity of theelectrical impulses suggests the pedicle screws are too close to spinalnerves. High conductivity is determined by recording electrical impulsesin the legs or arms of a patient after applying electrical impulses ofrelatively low amplitude to the pedicle screws.

Prior art “neurophysiology” techniques have several deficiencies. First,existing systems rely on the conductivity through a patient's body fromthe pedicle screw to electrodes in extremities or electrodes on the skinof the extremities. False negative values, low conductivity, can occurif the nerves or the skin do not conduct electricity well. Damagednerves can be relatively poor conductors of electricity. Second,electrical impulses of relatively high magnitudes must be used toovercome the resistance of the skin, muscles, and nerves. Stimulation byelectrical impulses of large amplitude can damage nerves. Third, thevariable resistance of patient's bodies leads to a relatively wide rangeof “normal” values recorded from the extremities. The wide range ofnormal values decreases the sensitivity and the specificity of the priorart technologies.

NuVasive, Inc. of San Diego, Calif. offers a product that uses “screwtest” technology to determine if a screw or similar device is beingpositioned close to a nerve during a surgical procedure. Surgeonstypically use NuVasive's system to stimulate screws, guidewires, andtaps placed into the pedicles of vertebrae. Recording surface electrodesare placed over the legs of the patient. Nerves conduct electricity veryefficiently, such that electrical stimulation of the metal objectsplaced into the vertebrae can be recorded in the legs.

Using the NuVasive system, an electrical charge is sent through thescrew, and a circle lights up on a computer screen giving a simplenumber to indicate the amount of charge reaching sensors placed on thepatient's leg muscles. A high number, such as a 20, suggests the screwis clear of the nerve. A lower reading, like a 3, indicates the nerve isbeing stimulated and the surgeon needs to consider moving the screw.Thus, the lower the amplitude needed to record activity in the legs, thecloser the metal objects are to the spinal nerves.

Research has shown that if the surface electrodes record electricalactivity with stimulation of less than 8 milliamps, the metal objectsare too close to the spinal nerves. The system can also be used in thecervical spine. The surface electrodes are placed on the arms forrecording stimulation of devices placed into the cervical spine.

The NuVasive system has a several shortcomings. For one, the system doesnot yield real-time data. Nor does the system allow for efficient,repeated stimulation of instruments that are turned. This is due to thefact that the NuVasive system uses a ball- tipped stimulating probe, andthe ball of the probe slips off the circular shaft of the instruments.In addition, while the system helps surgeons identify holes in thepedicle, it does not identify the location of the hole in the pedicle.Also, the instruments and screws that are placed into the spine cannottouch the skin, muscles, and subcutaneous tissues surrounding the spineduring electrical stimulation. If the metal instruments touch thesurrounding tissues during stimulation, the electricity can be shuntedfrom the vertebrae. Shunting of electricity can lead to false recordingsin the legs or arms (during stimulation in the cervical spine).Furthermore, the existing NuVasive system requires two different probes;one to stimulate screws and a second probe to stimulate wires.

SUMMARY OF THE INVENTION

This invention improves upon neurophysiological techniques throughprovision of several enhancement features. According to one aspect ofthis invention, stimulation of an instrument is possible while it isadvancing into the spine or elsewhere, alerting the surgeon to the firstsign the instrument or device (screw) may be too near a nerve. Earlyidentification of misdirected instruments or screws may thus helpprevent nerve damage.

A different aspect involves a directional probe that helps surgeonsdetermine the location of the hole in the pedicle. Yet a further aspectprovides an insulation sleeves to prevent shunting into the softtissues. According to a different improvement, the same probe to be usedto stimulate different devices, such as screws and wires.

One embodiment of the invention involves a clip that allows the use ofcontinuous monitoring during curette, pedicle probe, tap, pedicle screw,and/or lateral mass screw insertion. The clip fits around thecylindrical shafts of these and instruments used to insert devices,including screws. The clip allows the shafts of the instruments torotate without rotating the probe that sends electrical impulses for thetesting. The surgeon may rotate an instrument to insert a tap, forinstance, while an assistant repeatedly fires the probe. Thus, thesurgeon can detect a breach of the pedicle wall as soon as it occursrather than after the tap, etc. is fully inserted. Theoretically, earlydetection of a breach in the pedicle may prevent nerve injury andprevent enlarging a mal-aligned hole.

Other apparatus and methods of this invention improve upon existingneurophysiology technology in that electrical impulses are recorded fromthe spine rather than the extremities. Recording the impulses closer tothe stimulated pedicle screws overcomes the deficiencies of prior-arttechniques as outlined above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lateral view of the side of the current probe and a novelclip of the present invention;

FIG. 2 is an exploded view of the invention of FIG. 1;

FIG. 3A is a lateral view of a curette to “sound” the pedicle and theprobe with a clip attachment;

FIG. 3B is a lateral view of the probe of FIG. 1 attached to the curetteof FIG. 3A;

FIG. 3C is a cross section of the shaft of an instrument surrounded bythe novel clip of the present invention;

FIG. 4 is a lateral view of an alternative embodiment instrument shaft;

FIG. 5 is a lateral view of the embodiment of the instrument drawn inFIG. 4;

FIG. 6 is the lateral view of an instrument to retract the soft tissuesduring pedicle screw or instrument stimulation;

FIG. 7 shows the insulated soft tissue retractor drawn in FIG. 6;

FIG. 8A is a lateral view of the probe and the novel tip;

FIG. 8B is an axial cross section of a vertebra and probes with thenovel tips;

FIG. 9A is a lateral view of a screw driver, pedicle screw, and a novelinsulating sleeve;

FIG. 9B is a lateral view of apparatus drawn in FIG. 9A;

FIG. 9C is a cross section of the apparatus drawn in FIG. 9B;

FIG. 9D is a lateral view of the apparatus drawn in FIG. 9B;

FIG. 10A is a lateral view of an alternative embodiment of theinsulation sleeve, pedicle screw, and sleeve expander;

FIG. 10B is a lateral view of the apparatus drawn in FIG. 10A;

FIG. 10C is an axial cross section of the sleeve, screw, and sleeveexpander drawn in FIG. 10A;

FIG. 10D is an axial cross section of an alternative embodiment of thesleeve expander drawn in FIG. 10C;

FIG. 11A is a lateral view of an alternative embodiment of theinsulating sleeve;

FIG. 11B is an exploded view of the embodiment of the invention drawn inFIG. 11A;

FIG. 11C is a cross section of the apparatus drawn in FIG. 11A;

FIG. 12A is a lateral view of an alternative embodiment of the novelsleeve, a screw, and a screwdriver;

FIG. 12B is a lateral view of the apparatus drawn in FIG. 12A;

FIG. 13A is a sagittal cross section through an alternative embodimentof that drawn in FIG. 3;

FIG. 13B is a sagittal cross section through an alternative embodimentof that drawn in FIG. 13A;

FIG. 14A is a sagittal cross section of an alternative embodiment ofinvention drawn in FIG. 13B;

FIG. 14B is an exploded lateral view of the embodiment of the invention25 drawn in

FIG. 14A;

FIG. 14C is a sagittal cross section of an alternative embodiment of theinvention drawn in FIG. 14A;

FIG. 14D is an exploded lateral view of the embodiment of the inventiondrawn in FIG. 14C;

FIG. 15A is a sagittal cross section of an alternative embodiment of theinvention drawn in FIG. 14C;

FIG. 15B is an exploded lateral view of the embodiment of the inventiondrawn in FIG. 15A;

FIG. 16A is a lateral view of an alternative embodiment of the inventiondrawn in FIG. 14A;

FIG. 16B is an oblique view of an alternative embodiment of theinvention drawn in FIG. 16A;

FIG. 17A is a lateral view of an alternative embodiment of the inventiondrawn in FIG. 14A;

FIG. 17B is an exploded lateral view of the embodiment of the inventiondrawn in FIG. 17A;

FIG. 18 is an oblique view of a portion of a vertebra and the preferredapparatus;

FIG. 19A is a view of the dorsal aspect of a portion of a vertebra and arecording electrode;

FIG. 19B is a view of the dorsal aspect of a portion of a vertebra and arecording electrode;

FIG. 20A is a view of the dorsal aspect of a portion of a vertebra and a20 recording electrode on the inferior lateral surface of a pedicle;

FIG. 20B is a view of the dorsal aspect of a portion of a vertebra and arecording electrode;

FIG. 21A is an oblique view of the apparatus drawn in FIG. 18;

FIG. 21B is an exploded view of the apparatus drawn in FIG. 21A;

FIG. 21C is a view of the top of the connecting component, the recordingand stimulating electrodes;

FIG. 22 is an oblique view of a portion of a vertebra, a pedicleinstrument or screw, and the recording electrode;

FIG. 23 is an oblique view of a portion of a vertebra, a pedicle screw,recording and stimulating electrodes use in an alternative embodiment ofthe apparatus;

FIG. 24 is a view of apparatus according to the invention including astimulating probe;

FIG. 25 is a view of the posterior aspect of the spine;

FIG. 26 is the view of the front of an alternative embodiment of thedevice drawn in FIG. 24;

FIG. 27A is a posterior view of the spine similar to the view describedin FIG. 25;

FIG. 27B is a posterior view of the spine as described in FIG. 27A;

FIG. 28 is a posterior view of the spine, similar to the view drawn inFIG. 27B;

FIG. 29 is a posterior view of the spine similar to the view drawn inFIG. 28;

FIG. 30 is a posterior view of the spine, similar to the view drawn inFIG. 29, showing the alternative use of a reference electrode;

FIG. 31 is an axial view of a pedicle;

FIG. 32A is a lateral view of a needle-tipped stimulating or recordingelectrode;

FIG. 32B is a lateral view of an alternative embodiment of the tip ofthe electrode drawn in FIG. 32A;

FIG. 32C is a lateral view of an alternative embodiment of the tip ofthe electrode drawn in FIG. 32A;

FIG. 33 is an oblique view of an alternative embodiment of theinvention;

FIG. 34A is a lateral view of another embodiment of the invention drawnin FIG. 33;

FIG. 34B is an anterior view of the embodiment of the device drawn inFIG. 34A;

FIG. 34C is an oblique view of the embodiment of the device drawn inFIG. 34A;

FIG. 35 is an anterior view of another embodiment of the device drawn inFIG. 33;

FIG. 36 is a posterior view of a peripheral nerve and another embodimentof the invention; and

FIG. 37 is a lateral view of a nerve root retractor that stimulates thespinal nerves.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a lateral view of the side of the current probe 102 and anovel clip 104 according to this invention. One end of the clip snapsaround instruments. The second end of the clip snaps over the tip of theprobe. Alternatively, a second probe tip could be manufactured thatincorporates the novel tip end. FIG. 2 is a detached view of the probeand tip of FIG. 1.

FIG. 3A is a lateral view of a curette 302 used to “sound” the pedicleand the probe 102 with a clip attachment 104. The shaft of theinstrument 302 may be machined with a groove 310 to cooperate with theclip. FIG. 3B is a lateral view of the probe of FIG. 1 attached to thecurette of FIG. 3A. FIG. 3C is a cross section.

FIG. 4 is a lateral view of an alternative embodiment, wherein the shaftof the 20 tap has a raised portion 402 to cooperate with a clip 404. Theraised portion 402 avoids the stress riser created by a groove in theshaft. FIG. 5 is a lateral view of the embodiment of the instrumentdrawn in FIG. 4. The clip of the probe surrounds the shaft of thepedicle screw insertion tool. The clip rides on the enlargement of theshaft.

FIG. 6 is the lateral view of an instrument 602 used to retract the softtissues during pedicle screw or instrument stimulation. The retractioninstrument is made of plastic or other material that does not conductelectricity in the preferred embodiment.

As an alternative to the insulated soft tissue retractor of FIG. 6, aninsulated sleeve drawn in FIG. 7 may be used. FIG. 7 is an axial crosssection through a vertebra and the surrounding muscles, skin, andsubcutaneous tissues. A plastic sleeve would be particularly useful whenstimulating percutaneous guide pins inserted into the pedicles. Theinsulating sleeve 706 prevents the transmission of electricity from theguide pin to the muscles or surrounding soft tissue. A similar apparatuscould be used for testing modular taps. For example, the handle of a tapcould be removed, thus allowing the insulating sheath to be placed overthe tap.

Although the NuVasive monitoring system helps surgeons identify breachesof the walls of the pedicles, the system does not suggest where thepedicle wall has been breached. According to this invention, however,since the probe tip may be insulated circumferentially around themajority of the tip of the probe, the non-insulated portion of the tipcan be rotated within the pedicle to determine the direction thatrequires the least amount of stimulation to record activity in the lowerextremity.

FIG. 8A is a lateral view of the probe and a tip according to theinvention. The dark area of the tip conducts electricity. The remainderof the tip 806 is insulated to prevent the conduction of electricity.

FIG. 8B is an axial cross section of a vertebra and probes using thesetips. The medial walls of the pedicles have been breached. The probe onthe left side of the drawing has the non-insulted portion of the tipdirected toward the hole in the pedicle. The probe on the right side ofthe drawing has the insulated portion of the tip facing the hole in thepedicle. Less current will be required to stimulate the nerves on theleft side of the drawing. For example, the surface electrodes couldrecord activity in the lower extremity with stimulation of the probe at4 milliamps with the exposed (conducting) area of the probe directedtoward the medial wall of the pedicle (probe on the left side of thedrawing) and the surface electrodes could record electrical activity inthe lower extremities with stimulation of the probe at 10 milliamps withthe exposed (conducting) area of the probe directed toward the lateralwall of the pedicle (probe on the right side of the drawing). Thus, thesurgeon knows the medial wall of the pedicle has been breached.Consequently, the surgeon knows to redirect the pedicle screw morelaterally, away from the holes in the pedicle.

FIG. 9A is a lateral view of a screwdriver 902, pedicle screw 904, andan insulating sleeve 906. The insulating sleeve is preferablyconstructed of a flexible material that does not conduct electricity.For example, the sleeve could be made of plastic or natural or syntheticrubber. The sleeve can be seen folded back over itself at 908 just abovethe pedicle screw.

FIG. 9B is a lateral view of apparatus drawn in FIG. 9A. The insulatingsleeve 906 has been unfolded and placed over the head of the pediclescrew. The insulating sleeve prevents the transmission of electricityinto the tissues that surround the spine. Electricity from stimulatingthe shaft of the screwdriver exits through the threads of the screw. Thesleeve enables the screwdriver to lie against the muscles of the spinewithout stimulating the muscles of the spine.

FIG. 9C is a cross section of the apparatus drawn in FIG. 9B. Theflexible insulation sleeve can be stretched to fit tightly against theshaft of the screwdriver and the pedicle screw.

FIG. 9D is a lateral view of the apparatus drawn in FIG. 9B. Theinsulation sleeve may be removed by pulling on a cord 980 which tearsthe sleeve. Alternative mechanisms can be used to remove the sleeve fromthe screw. For example, the sleeve could be pulled from the screw whileexerting counter pressure on the screw by the screwdriver. The sleevecould also be folded on itself as the sleeve is removed from the screw.

FIG. 10A is a lateral view of an alternative embodiment of an insulatingsleeve 1002, pedicle screw 1004, and screwdriver with a sleeve expander1006. The sleeve is drawn in its expanded shape. The tip of the sleeveexpander fits into the pedicle screw. In the preferred embodiment, thesleeve expander is flush with the top of the pedicle screw. The sleevein this embodiment of the device is made of material that plasticallydeforms at its tip. The sleeve does not transmit electricity.

FIG. 10B is a lateral view of the apparatus drawn in FIG. 10A with thesleeve in its contracted shape. The tip of the sleeve contracts tosurround the head of the pedicle screw. Ideally the sleeve is more rigidthan sleeve drawn in FIG. 9A. The rigidity of the sleeve enables it tobe forced over the screw by pushing on the top of the sleeve. Thisembodiment of the device would be easier to use after the screw has beenplaced into the spine.

FIG. 10C is an axial cross section of the sleeve 1002, screw 1004, andsleeve expander 1006 in FIG. 10A. The sleeve expander 1006 fits into theopening in the pedicle screw. FIG. 10D is an axial cross section of analternative embodiment of the sleeve expander 1016, a screw 1014, andthe sleeve 1012. The tip of the sleeve expander in this case is round tofit in the circular opening in the pedicle screw.

FIG. 11A is a lateral view of an alternative embodiment of theinsulating sleeve 1108 assembled over a pedicle screw 1110. FIG. 11B isan exploded cross-sectional view of the embodiment of the inventiondrawn in FIG. 11A. FIG. 11C is a cross section of the apparatus drawn inFIG. 11A. FIG. 12A is a lateral view of an alternative embodiment of thenovel sleeve 1202, a screw 1204, and a screwdriver 1206. The insulatingsleeve is placed over the pedicle screw and screwdriver prior toinsertion of the pedicle screw into the spine.

FIG. 12B is a lateral view of the apparatus drawn in FIG. 12A. Thesleeve has been pulled off of the pedicle screw. Longitudinal force onthe sleeve may be used to split the sleeve along a pre-stressed area inthe sleeve.

FIG. 13A is a sagittal cross section through an alternative embodimentof the invention, wherein a probe 1302 is placed into the center of aninstrument 1304. The illustration shows application of the probe to atap. Placing the instrument onto or into the center of the instrumentallows rotation of the instrument during repeated stimulation of theinstrument.

FIG. 13B is a sagittal cross section through an alternative embodimentof that drawn in FIG. 13A. The probe connects to an intermediate piece1330 that connects to the center of the instrument.

FIG. 14A is a sagittal cross section of an alternative embodiment ofinvention drawn in FIG. 13B. The spherical end of an electrode 1404 iscaptured in the instrument by a cannulated, threaded cap 1406. The shaftof the instrument 1410 conducts electricity. The joint between the tipof the electrode allows movement between the electrode and theinstrument, while maintaining continuous contact between the twocomponents. FIG. 14B is an exploded lateral view of the embodiment ofthe invention drawn in FIG. 14A.

FIG. 14C is a sagittal cross section of an alternative embodiment of theinvention utilizing a flat-tipped electrode 1440 captured by a threadedcomponent 1444. The joint between the electrode and the instrumentallows rotation. FIG. 14D is an exploded lateral view of the embodimentof the invention drawn in FIG. 14C. Connections between electrodes ofalternative shaped tips and instruments of alternative shapes arecontemplated so long as the joints between the components permitrotation and keep the two components in contact.

FIG. 15A is a sagittal cross section of an alternative embodiment of theinvention, wherein an electrode 1550 is threaded over the shaft of theinstrument 1552. The threaded connection between the electrode and theinstrument holds the two components together. Rotation may occur acrossthe flat surfaces of the two components. FIG. 15B is an exploded lateralview of the embodiment of the invention drawn in FIG. 15A.

FIG. 16A is a lateral view of an alternative embodiment of the inventiondrawn in FIG. 14A. A wire 1660 for the electrode is connected to aratcheting component 1664 on the shaft of the instrument. The ratchetingcomponent permits advancement of screws and taps with small rotations ofthe handle of the instrument forward and backward. The electrode doesnot wrap around the instrument because the handle of the instrument doesnot require rotation through 360 degrees.

FIG. 16B is an oblique view of an alternative embodiment of theinvention drawn in FIG. 16A. The electrode is connected to a conductingcomponent within the handle of the instrument. The conducting componenttransmits electrical impulses between the electrode and the shaft of theinstrument. The ratcheting mechanism prevents wrapping the cord of theelectrode around the instrument as the instrument is rotated.

FIG. 17A is a lateral view of an alternative embodiment of the inventionincluding an electrode 1780 connected to a collar that rotates aroundthe shaft of the instrument. The collar is held between projections fromthe shaft of the instrument. The collar remains in contact with theshaft of the instrument. Rotation between the shaft of the instrumentand the collar prevents wrapping the cord of the electrode around theinstrument as a screw or tap is advanced. FIG. 17B is an explodedlateral view of the embodiment of the invention drawn in FIG. 17A. Therotating collar is held on the shaft of the instrument by a removablethreaded component 1788.

FIG. 18 is an oblique view of a portion of a vertebra and preferredapparatus including a recording electrode 1802 placed around a portionof the pedicle of a vertebra 1800. The recording electrode is connectedto a monitor 1804. The area 1806 represents a pedicle probe, tap, screw,or other instrument that will be placed into the pedicle. The pedicleinstrument or screw is connected to a stimulating electrode. Therecording and stimulating electrodes can be connected by third component1810. The connecting 15 component is represented by the area of thedrawing with diagonal lines. In the preferred embodiment, the connectingcomponent 1810 is radiolucent and made of a material that conductselectricity poorly.

FIG. 19A is a view of the dorsal aspect of a portion of a vertebra and arecording electrode 1802. The lamina of the vertebra has been removed tobetter illustrate the pedicles of the vertebra. The arms of therecording electrode can be seen surrounding the inferior, medial, andlateral surfaces of the pedicle. The recording electrode was insertedfrom the inferior and/or lateral side of the vertebra.

FIG. 19B is a view of the dorsal aspect of a portion of a vertebra and arecording electrode 1802. The recording electrode can be seen over themedial, superior, and inferior surfaces of a pedicle. The recordingelectrode was inserted from the medial side of the pedicle. Alaminectomy could be performed to aid placement of the electrode.

FIG. 20A is a view of the dorsal aspect of a portion of a vertebra and arecording electrode 1802 on the inferior lateral surface of a pedicle.FIG. 20B is a view of the dorsal aspect of a portion of a vertebra and arecording electrode. The recording electrode has been advanced over thepedicle. The arms of the recording electrode can be spring loaded toease insertion of the electrode over the pedicle.

FIG. 21A is an oblique view of the apparatus drawn in FIG. 18. Theconnector 1810 aligns the instrument or screw to be inserted into thepedicle with the arms of the recording electrode. For example, pediclescrews can be directed into the center of the arms of the recordingelectrode. Thus, if the arms of the recording electrode surround aportion of the pedicle, the pedicle screw or instrument can be directedinto the center of the pedicle.

FIG. 21B is an exploded view of the apparatus drawn in FIG. 21A. Aremovable handle is also illustrated. The removable handle can be placedover the recording electrode after placement of the connecting componentover the recording component.

FIG. 21C is a view of the top of the connecting component, the recordingand stimulating electrodes. The radiolucent connecting component allowssurgeons to view insertion of the stimulating electrode between the armsof the recording electrodes with fluoroscopy. The arms of the recordingelectrode surround a portion of the pedicle.

FIG. 22 is an oblique view of a portion of a vertebra, a pedicleinstrument or screw, and the recording electrode. The pedicle instrumentcan be seen penetrating the wall of the pedicle. The recording electrodecan be moved up and down or around the pedicle to aid detection of theelectrical impulse.

FIG. 23 is an oblique view of a portion of a vertebra, a pedicle screw,recording and stimulating electrodes use in an alternative embodiment ofthe apparatus. The recording electrode detects impulses in the spinalcanal, nerves, muscles, vertebrae, and other spinal tissues or tissuesthat surround the spine. For example, the recording electrode could beplaced on a spinal nerve, or the thecal sac. Penetration of the pediclescrew or instrument would be predicted by recording electrical impulsesfrom the spinal nerve or thecal sac after stimulating the pedicleinstrument with electrical impulses with relatively low amplitudes. Therecording electrode could also be placed in other spinal tissues such asthe paraspinal muscles. Fluid or other material could be placed aroundthe pedicle to aid the conduction of electrical impulses. For example,saline could be placed into the spinal canal during the stimulation andrecording of the electrical impulses.

The invention also anticipates reversing the stimulating and therecording electrodes. That is, electrical impulses could be recordedfrom pedicle screws or instruments after stimulating a portion of thespine. For example, the outer wall of the pedicle could be stimulated.Additionally, the sensitivity and specificity of the apparatus, as wellas prior art apparatus, could be improved by measuring the time betweenstimulation and recording the electrical impulses. Relatively high ratesof electrical conduction suggest the pedicle screw or instrument lies onor too near a nerve.

FIG. 24 is a view of apparatus according to the invention including astimulating probe 2406 used to stimulate the spinal nerves (or othernerves). The stimulating probe is inserted into a port on the devicemarked “Stimulus”. A recording cable 2408 is inserted into a port on thedevice marked “Instrument”. The recording cable attaches to aninstrument placed in the pedicle. For example, the “instrument”recording cable could be attached to the ratcheting instrument describedin FIG. 16A. The ratcheting instrument is used to insert screws or tapsinto the vertebrae.

A second recording cable 2410 is inserted into a port on the devicemarked “Muscle”. The “Muscle” recording cable may include a bundle ofwires. The wires within the “Muscle” recording cable attach to leadsplaced over muscles. For example, the “muscle” leads could be placedover the myotomes of both lower extremities or both upper extremities.Alternatively, the “Muscle” cable could be attached to leads over thegluteal muscles, the paraspinal muscles, or tissues of the body.

A green indicator light indicates safe placement of the pedicleinstrument. The green light illuminates if the “Muscle” recording cablesends an electrical impulse into the device after stimulation of aspinal nerve (alternatively other nerves could be stimulated) and the“Instrument” recording cable does not send an electrical impulse intothe device after stimulation of the spinal nerve. A 6 mA stimulus couldbe delivered to the stimulus probe. Alternative stimuli between 0.01 mAto 40 mA could be delivered.

A red indicator light indicates a potentially misplaced pedicleinstrument. The red light illuminates if the “Instrument” recordingcable sends an electrical impulse into the device after stimulation ofthe spinal nerve or the “Muscle” recording cable fails to send anelectrical impulse into the device. Two additional lights are used todetermine why the red light illuminated. A “Muscle” light illuminates ifthe “Muscle” recording cable fails to send an electrical impulse intothe device. Failure of the “muscle” recording cable to send anelectrical impulse into the device suggests the nerve was not properlystimulated. An “Instrument” light illuminates if the “Instrument” cablesends an electrical impulse into the device. Illumination of the“Instrument” light alerts the surgeon the pedicle instrument hasreceived an electrical impulse. The pedicle instrument receives anelectrical impulse, if the instrument has breached the walls of thepedicle and the instrument is lying against the stimulated nerve. Thedevice may also have ports that receive ground and reference electrodes.

Existing systems monitor all of the myotomes of both extremities. Anelectrical stimulus is delivered to the instrument within the pedicle.Detection of the electrical impulse after low levels of stimulation, forexample 8 mA, in any myotome is indication of a potentially misplacedpedicle instrument. A preferred embodiment of this invention recordsfrom the instrument or screw within the pedicle rather than stimulatingthe instrument or screw within the pedicle. Recording leads over themuscles are used to confirm an electrical impulse has been applied to aspinal nerve (or other nerve). As such, recording a stimulus from anymuscle in the extremities or potentially other muscles such as thegluteal or paraspinal muscles indicates the stimulus has been properlydelivered. Recording from fewer, multiply innervated muscles, simplifiesthe device. Recording from fewer muscles and recording from the glutealor paraspinal muscles also assists the surgeon. The present inventiondecreases the amount of time surgeons must spend applying the recordingleads over multiple myotomes of both extremities while using prior artsystems. The simplicity of the device enables surgeons to test andmonitor their patients. The device does not require a highly compensatedNeurophysiologist to interpret the data. Other embodiments of theinvention eliminate the need to monitor any of the muscles.

FIG. 25 is a view of the posterior aspect of the spine. The lamina havebeen removed to better illustrate the pedicles 2502 and the nerves 2504.The black circle in the center of one of the white circles indicates thecross section of an instrument within the pedicle (for example) a screw,tap, or curette.

In the embodiment of the invention depicted in FIG. 24, an electricalstimulus is delivered to the lower spinal nerve at point S. A recordingelectrode is attached at R to the instrument within pedicle. One or moreadditional recording electrodes are placed over muscles. A secondstimulus is delivered to the spinal nerve at S′, or, alternatively atS″. If the pedicle instrument breaches the medial wall (spinal canalside) or the inferior wall of the pedicle, and the instrument liesagainst the spinal nerve, stimulation of the lower spinal nerve willstimulate the instrument in the pedicle. If the pedicle instrumentbreaches the lateral or superior wall of the pedicle, and the instrumentlies against the spinal nerve, stimulation of the upper spinal nervewill stimulate the instrument within the pedicle. Instruments inadjacent pedicles on the same side of the spine may be testedsimultaneously by stimulating a single spinal nerve. For example,stimulation of the L4 nerve simultaneously tests the integrity of themedial and inferior walls of the L4 pedicle and the superior and lateralwalls of the L5 pedicle. Simultaneous testing of instruments within thepedicles requires a multi-channel device.

Prior art systems may detect a hole or a crack in a pedicle, but they donot indicate the location of the crack or hole in the pedicle. Ifsurgeons know the location of the hole in the pedicle, then they canreposition a screw and safely direct the screw away from the hole in thepedicle. This invention helps surgeons determine if the misplacedpedicle instrument was placed through the inferior and/or the medialsurface of the pedicle or through the superior and/or lateral wall ofthe pedicle.

FIG. 26 is the view of the front of an alternative embodiment of thedevice drawn in FIG. 24. The multi-channel device can be used tosimultaneously test instruments in more than one pedicle. The cablesextending from ports on right side of the device marked “Instrument 1”and “Instrument 2” can be attached to instruments in different pedicles.The stimulus probe can be used to deliver electrical impulses to aspinal nerve. The cables extending from the ports marked “Muscle 1 &Muscle 2” can be attached to surface electrodes over muscles supplied bythe stimulated nerve. A single recording electrode may also be used whentesting the instruments in two pedicle screws. For example, the cableattached to “Instrument1” could be attached to a tap in the left L4pedicle.

The cable attached to “Instrument 2” could be attached to a screwdriverattached to a pedicle screw in the left L5 pedicle. The cables extendingfrom the “Muscle 1” and/or “Muscle 2” ports could be attached to needleelectrodes placed into the Gluteus Medius and the Gluteus MaximusMuscles of the left buttock. The Gluteus Medius is innervated by thesuperior gluteal nerve. The superior gluteal nerve arises from the L4,L5, & S1 nerves. The Gluteus Maximus is innervated by the inferiorgluteal nerve. The inferior gluteal nerve arises from the L5, S1, and S2nerves. Surface electrodes could be used rather than needle electrodes.A stimulus could be applied to the left L4 nerve root. The L4 nerve rootcourses along the inferior and medial surfaces of the L4 pedicle, andthe superior and lateral portion of the L5 pedicle.

The indicator lights are similar to the indicator lights drawn in FIG.24. If both green lights illuminate, then device did not detectelectrical impulses from either instrument in the pedicles, and thedevice detected an electrical impulse from the recorded muscles. Thedevice may use a reference recording lead to compare to the musclerecording lead. The device may contain a microprocessor. If the musclerecording lead receives a much stronger impulse than the referenceelectrode receives, then the nerve has likely been stimulated properly.Alternatively, the microprocessor may compare the impulses received bythe recording electrodes to reference values. The reference valuesenable the device to indicate if the nerve has been properly stimulatedor the soft tissues around the nerve were mistakenly stimulated. Thedevice may use a ground lead.

The red light by the large number one will illuminate if the instrumentattached to the cable from the “Instrument 1” port receives anelectrical impulse or the device fails to receive an impulse from bothor either “Muscle” recording electrodes. Similarly, the red light by thelarge number two will illuminate if the instrument attached to the cablefrom the “Instrument 2” port receives an electrical impulse or thedevice fails to receive an impulse from both or either “Muscle”recording electrodes. The “Instrument 1 & 2” and the “Muscle 1 & 2”lights are used as described in the text of FIG. 24, to indicate if theinstruments have been stimulated or the muscles were not stimulated.

FIG. 27A is a posterior view of the spine similar to the view describedin FIG. 25. The dark circles represent instruments in the pedicles. R1and R2 represent recording electrodes that are attached to theinstruments in the pedicles. S1, S2, & S3 represent a few of thepossible stimulation sites. The figure illustrates a nerve may bestimulated below the pedicle, at the level of the pedicle, or above thepedicle. Stimulation of the nerve below the pedicle relies ontransmission of the impulse in a caudal direction to test the superiorand lateral aspects of the pedicle below the stimulated nerve andtransmission of the impulse in a caudal direction to stimulate themuscle. Stimulation of the nerve below the pedicle relies ontransmission of the impulse in a cephalic direction to test the inferiorand medial surfaces of the pedicle above the stimulated nerve. Spinalnerves carry electrical impulses in both cephalic and caudal directions.Motor portions of the nerves transmit impulses away from the spinal cordto the muscles (caudal direction). Sensory portions of the nervestransmit impulses from the sensation receptors to the spinal cord(cephalic direction). The device drawn in FIG. 26 could be used to testthe instruments in the adjacent pedicles drawn in FIG. 27A. A singlestimulus delivered at S3 would test the instruments in both pedicles.Additional stimulus sites could be used to complete the testing. Forexample, stimulus sites S4 and S2 could be used to complete the testing.

FIG. 27B is a posterior view of the spine as described in FIG. 27A. Thecross sections of pedicle instruments are seen in all of the pedicles.The drawing illustrates other embodiments of the invention. Theembodiments drawn in FIG. 27B do not require monitoring the muscles inthe extremities. In one embodiment of the invention the recordingelectrodes are placed in or over the nerves. Techniques well know tothose specialists who perform EMG testing could be used to locate thenerves. Alternatively, the electrodes could be placed on or in thenerves under direct observation.

A stimulus is applied at 51. The recording electrodes are attached tothe instrument in the pedicle (R1) and another portion of the stimulatednerve. If the R2 electrode detects the stimulated impulse and the R1electrode does not detect the impulse, then it is unlikely the pedicleinstrument is contacting the stimulated nerve. A multi-channel devicecould be used to test the instruments in more than one pediclesimultaneously. The R2 electrode could be placed in a spinal nerve or aperipheral nerve that has components that arise from the stimulatednerve. For example, for testing the pedicles in the lumbar spine, the R2electrode could be placed in the sciatic nerve (L4, L5, S1, S2, & S3) orbranches from the sciatic nerve, the femoral nerve (L2, L3, & L4) orbranches from the femoral nerve, or other nerves. The spinal nervecomponents that form the sciatic and femoral nerves are listed inparentheses behind the words sciatic nerve and femoral nerverespectively. Naturally other nerves would be stimulated and recordedwhen testing instruments in the cervical and thoracic spine.

The invention is more sensitive and more accurate than prior-artdevices. Prior-art devices may record a false positive if electricalimpulses are delivered through a crack in the pedicle, but theinstrument is contained within the pedicle. The present invention allowstesting with smaller electrical impulses. The smaller impulses are lesslikely to stimulate a pedicle instrument through cracks in the pedicle.Prior art devices may record a false negative if the recordingelectrodes over the muscles in the extremities fail to detect animpulse. As noted previously, nerves that conduct impulses poorly, poorconduction through the surface electrodes, etc., may falsely indicatethe instrument is safely contained in the pedicle.

Prior-art systems generally send multiple stimuli of increasingamplitude into the instrument within the pedicle. Prior art systemsattempt to record the amount of stimuli necessary to record the impulseover the lower extremities. Recording an impulse over the lowerextremities decreases the probability of a false negative result.Stimulating pedicle instruments with multiple stimuli with increasingamplitude is time consuming and requires sophisticated software. Thepresent invention improves upon prior art devices by generally onlyrequiring the application of a single stimulus per pedicle instrumentundergoing testing. Some embodiments of the invention allow testingpedicle instruments in multiple vertebrae with the application of asingle stimulus.

Note that the invention may also be used to test nerves while retractingnerves or performing other spinal procedures. The distance between S1and R2 could be predetermined. In fact, S1 and R2 could extend from thesame instrument. Electrical impulses could be periodically delivered tothe nerve at S1 during surgery. For example, the electrical impulsescould be delivered at a frequency of one per minute. The microprocessorwithin the monitor could signal an alarm, for example, illuminate alight bulb, if the amplitude of the impulse detected at R2 decreasedwhen compared to a reference amplitude obtained by stimulating the nervebefore manipulating the nerve during the operation. The microprocessorcould also cause an alarm to signal if the time between the stimulusdelivered at S1 and recorded at R2 increased when compared to areference time obtained for the nerve before manipulating the nerveduring the operation.

Standard reference amplitudes and velocities may also be preprogrammedinto the microprocessor. Standard reference velocities require fixeddistances between S1 and R2. The S1 impulse could be delivered through anerve root retractor or a stimulus probe. A stimulus deliveringretractor is drawn in FIG. 37. As noted above, R2 may lie anywhere alongthe course of the spinal nerve, nerves supplied by the spinal nerve, ormuscles supplied by the spinal nerve. The device alerts surgeons ofpotential nerve injury before the nerve injury occurs. For example,excessive retraction of a nerve root may injure the nerve root. Thedevice detects diminished nerve function within seconds or minutes ofthe excessive retraction. Embodiments of the invention for use withperipheral nerves are described in FIG. 36.

In the drawings, R4 represents an alternative recording position. One ormore R4 electrodes could be placed over or in muscles of the bodyincluding muscles in the extremities, the muscles in the buttock, themuscles about the shoulder, or muscles about the spine. In contrast toprior-art devices, the R4 electrode may be used to confirm the nerve hasbeen properly stimulated. Any muscle innervated by the stimulated musclemay be monitored. A single muscle that is supplied by multiple nerveroots may be monitored while testing instruments in pedicles atdifferent levels of the spine. For example, the Gluteus Medius musclecould be monitored to confirm the L4, L5, or S1 nerves have beensuccessfully stimulated. The gluteal muscles and the skin over themuscles are easily reached during surgeries on the lumbar spine.Prior-art systems require monitoring of many muscles of the body.Failure to detect stimulation of one of the muscles may lead to a falsenegative reading. A false negative reading fails to properly detect aninstrument, such as a pedicle screw, is compressing or injuring a nerve.Prior-art systems typically require monitoring over four separatelocations over each extremity. Preparing the skin over multiple sitesand placing the electrodes over multiple sites is time consuming.

The present invention alerts surgeons if the R4 electrode is improperlyplaced or if the R4 electrode/electrodes has/have shifted during theoperation. The red light on the device and the muscle light on thedevice illuminate if the R4 electrode does not record an impulse. Thenovel invention enables surgeons to monitor the paraspinal muscles. Theparaspinal muscles area easily accessible in the surgical field. Priorart devices do not use the paraspinal muscles. Surgical exposure of thespine may injure the paraspinal muscles or the nerves to the muscles.Injury to the nerves to the paraspinal muscles or injury of theparaspinal muscles may cause prior art devices and methods to yield afalse negative result, if the devices fail to record an impulse. Failureof prior art methods and devices to detect stimulation of the paraspinalmuscles could indicate: (a) that the pedicle instrument is containedwithin the pedicle, (b) the nerve to the paraspinal muscle is notfunctioning properly, (c) the paraspinal muscles are not functioningproperly or, (d) the stimulated muscle has not been recorded.Explanations (b), (c), and (d) lead to false negative results. Thus,prior-art systems do not monitor the paraspinal muscles. The presentinvention alerts the surgeon if injury to the nerves to the paraspinalmuscles or the paraspinal muscles precludes monitoring the muscles, Ifthe surgeon is unable to detect recordings from the paraspinal musclesafter delivering a stimulus to the nerves, then the surgeon is alertedto monitor other muscles, such as the gluteal muscles. The ventrally,segmentally, innervated intertransversalis muscles are monitored in oneembodiment of the invention. Other paraspinal muscles may be monitored.

FIG. 28 is a posterior view of the spine, similar to the view drawn inFIG. 27B. An alternative embodiment of the invention is illustrated inthe drawing. S1 represents stimulation of a peripheral nerve such as thesciatic nerve, femoral nerve, branches the sciatic nerve, branches ofthe femoral nerve, or other peripheral nerve. R3 & R4 representrecording sites on or in the spinal nerves. Alternative R3 & R4 sitesinclude nerves within the thecal sac, the spinal cord, or the brain. TheR3 & R4 sites are monitored to confirm the nerve has been stimulatedcorrectly. The R1 & R2 are monitored to detect stimulation of theinstruments within the pedicles. A single electrical stimulus from S1could be used to test multiple pedicles simultaneously. Stimulation ofthe sciatic nerve may allow simultaneous testing of the pedicles nearthe L4, L5, S1, S2, & S3 nerves. Stimulation of the femoral nerve mayallow testing of the pedicles near the L2, L3, and L4 nerves. Amulti-channel device allows simultaneous testing of multiple pedicles.

FIG. 29 is a posterior view of the spine similar to the view drawn inFIG. 28. The alternative embodiment of the invention stimulates multiplespinal nerves simultaneously. Si represents a stimulus delivered overthe nerves in the thecal sac, the spinal cord, or the brain. Anelectrical or magnetic stimulus may be used. R1B, R2B, R3B, & R4B arerecording sites to confirm the spinal nerves near the pediclesundergoing testing are properly stimulated. R1A, R2A, R3A, & R4A arerecording sites from the instruments that lie within the pedicles. IfR1B, R2B, R3B, or R4B fail to detect an impulse, the device will alertthe surgeon that the pedicle instruments at the R1A, R2A, R3A, or R4Asites respectively, has not been adequately tested. Failure to detect animpulse at a RnB site signals the stimulus was not applied to thesurface of the pedicle by the nerve monitored by the RnB electrode. A S1needle electrode may be placed through the dura. The S1 site may becephalad or caudal to the tested pedicles. If all RB sites recordimpulses and none of the RA sites record impulses, then all of theinstruments are likely contained within the pedicles. A multi-channeldevice, with at least four groups of alarm lights like those illustratedin FIG. 24, could be used in this embodiment of the invention.

FIG. 30 is a posterior view of the spine, similar to the view drawn inFIG. 29, showing the alternative use of a reference electrode. Amicroprocessor within the device compares the impulse detected by the R2electrode to the impulse detected by the reference (R3) electrode. Themicroprocessor triggers an alarm, such as illuminating a light bulb, ifthe stimulus received by R2 is below a preset value or the stimulusreceived by R2 is near or below that received by R3. The alarm alertsthe surgeon that the electrodes at the R2 or S1 sites are not properlycontacting the spinal nerve.

FIG. 31 is an axial view of a pedicle. The drawing illustrates analternative embodiment of the invention. The black circle represents thecross section of an instrument in the pedicle. S1 represents astimulation site. R1 represents a recording site on the instrument inthe pedicle. R2 represent a recording site on the pedicle. If the R1electrode detects a smaller signal than the R2 electrode the instrumentis likely contained in the pedicle.

FIG. 32A is a lateral view of a needle-tipped stimulating or recordingelectrode. The area of the drawing with diagonal lines representsinsulating material. The needle tipped electrode is generally placed innerves or muscles. FIG. 32B is a lateral view of an alternativeembodiment of the tip of the electrode drawn in FIG. 32A. The balledtipped probe is generally placed on nerves or muscles. FIG. 32C is alateral view of an alternative embodiment of the tip of the electrodedrawn in FIG. 32A. The curved tip is easier to insert through theneuroforamina. The tip may help the surgeon direct the electrode to theS1 position drawn in FIG. 30.

FIG. 33 is an oblique view of an alternative embodiment of theinvention. This embodiment of the invention demonstrates the use ofstimulating (S1) and recording (R1) electrodes in an instrument. Forexample the instrument may be a cannula as drawn in

FIG. 33. Other than the electrodes, the instrument is made of anon-electrical conducting material in the preferred embodiment of thedevice. A monitor with microprocessor measures the amplitude andvelocity of an impulse delivered from S1 to R1. Rapid transfer of a highamplitude impulse suggests the cannula is against a tissue that readilytransfers impulses. Nerves transmit impulses better than musclestransmit impulses. The novel cannula could be used to alert surgeonswhen the instrument is against a nerve. Surgeons could use the novelcannula to navigate between the nerves in muscles. For example, surgeonscould use the device for trans-psoas approaches to the spine.

FIG. 34A is a lateral view of another embodiment of the invention drawnin FIG. 33.

Recording and stimulating electrodes are used in the walls of a styletor a blunt dissector. Other than the electrodes, the stylet or dissectoris made of a material that conducts electricity poorly. The stylet canbe used within a cannula. The blunt tip helps surgeons separate thefibers of muscles. The electrodes and the monitor alert surgeons whenthe instrument lies against a nerve. FIG. 34B is an anterior view of theembodiment of the device drawn in FIG. 34A.

FIG. 34C is an oblique view of the embodiment of the device drawn inFIG. 34A. FIG. 35 is an anterior view of another embodiment of thedevice drawn in FIG. 33. The electrodes are incorporated into the endsof a retractor.

FIG. 36 is a posterior view of a peripheral nerve and another embodimentof the invention. This embodiment of the invention may be used toprotect peripheral nerves during non-spinal operations. The nerve isstimulated at one location S1. Recording electrodes/electrode are placedin another location along the nerve or a branch of the nerve (R1).Alternatively recording electrodes/electrode may be placed in musclesthat are supplied by the stimulated nerve (R2). A device, with amicroprocessor, delivers electrical impulses at S1 periodically duringthe operation. For example, the device may deliver one impulse perminute.

The device measures the amplitude of the impulses recorded at R1 and/orR2 and the time between the delivery of the stimulus and recording ofthe stimulus. The device triggers an alarm, for example illuminates alight bulb, if the amplitude or velocity of the transmitted stimulusdeteriorates during the surgical procedure.

The microprocessor may also be programmed to compare the recorded valuesfor the stimulus to standard values. The distance between S1 and R1 orR2 could be fixed or measured to enable the microprocessor to calculatevelocity figures. For example, this embodiment of the device could beused during hip replacement surgery. A needle electrode (S1) could beplaced into the sciatic nerve at the level of the sciatic notch. The S1electrode could be sutured into place. Alternatively, the mechanisms useto hold pacemaker electrodes in position could be used to hold the S₁electrode in the tissues near the sciatic nerve while the tip of the S1electrode lies in the nerve. The device would quickly alarm the surgeonif sciatic nerve function deteriorated during surgery. The device wouldalert the surgeon to diminish traction on the sciatic nerve before theinjury became permanent. This embodiment may be used on other peripheralnerves in the body. It may also be used to detect additional causes ofnerve injury such as pressure on the nerve or surgical dissection aroundthe nerve.

FIG. 37 is a lateral view of a nerve root retractor that stimulates thespinal nerves. The retractor can be used to deliver the stimulus at theS1 site as described in FIG. 30.

According to this invention, electric impulses may be recorded from aninstrument placed into and possibly through the pedicle of a vertebra.Peripheral nerves, spinal nerves, the sciatic nerve, the femoral nerve,or a plexus of nerves may be stimulated. Recording electrodes are alsoplaced over spinal nerves. A recording electrode may be placed throughthe dura. If the recording electrode over, or within, a nerve detects animpulse transmitted through the nerve and the recording electrode on aninstrument placed into a pedicle does not detect an impulse, then it islikely the instrument within the pedicle does not breach the walls ofthe pedicle. Alternatively, the spinal nerves could be stimulated withrecording electrodes placed over or in peripheral nerves, the nerves inthe thecal sac, and the instrument/instruments in the pedicles.

Stimulation and/or recording electrodes can be used over the dura orthrough the dura cephald and/or caudal to the level the pedicle screw orscrews are inserted. Multiple pedicle screws could be testedsimultaneously by a single stimulating impulse. For example, atrans-dural stimulating electrode could be placed cephald to the pediclescrews. A second trans-dural recording electrode could be placed caudalto the pedicle screws. Alternatively, multiple recording electrodescould be placed over or in the spinal nerves near the pedicle screws.The recording electrodes listed above could be changed to stimulatingelectrodes and the stimulating electrodes listed above could be changedto recording electrodes. If recording electrodes placed on instrumentswithin the pedicles do not detect an electrical impulse, but therecording electrodes over or within the nerves detect an impulse, thenthe screws, curettes, or taps are likely within the pedicles. Testing ofthe invention will likely determine thresholds (for stimulation andrecording) at which penetration of the pedicle wall by an instrument isunlikely. Techniques well known to those who perform EMG testing couldbe used to help locate spinal and peripheral nerves.

An electrode placed over or within a myotome may be used to confirmstimulation of a nerve. For example, if an electrode over the L5 myotomedetects an impulse applied to the L5 nerve and a recording electrodefrom an instrument in a pedicle near the L5 nerve does not record animpulse, it is unlikely the instrument within the pedicle near the L5nerve penetrates the wall of the pedicle. The invention eliminates theneed for repeated stimulation at successively higher impulses as used inprior art systems. Prior art systems use successively higher impulses torecord a value in the extremities in an effort to avoid a falsenegative. Failure to record a stimulus over the myotome in prior artsystems may confirm the instrument does not penetrate the walls of thepedicle. Alternatively, failure to record a stimulus over the myotome inprior art systems may indicate a problem with the conductivity of thenerve, the junction between skin and the electrode, or other technicalproblem.

Recording and/or stimulating electrodes can be placed in or over thetissues about the spine including the disc, the gluteal muscles, musclesabout the hip or shoulder girdle, or the extremities.

Velocity calculations and measurements (of transmittance of theelectrical impulse) may also be used. A single monitor or instrument mayhave recording and stimulating electrodes. A fixed distance between therecording and stimulating electrodes would ease velocity calculations.For example, a non-conducting cannula with one or more stimulatingelectrodes and one or more recording electrodes may be used intranspsoas approaches. An impulse that travels with high velocity fromthe stimulating electrode to the recording electrode suggests thecannula is near or against a nerve. Stimulation may be in the range of0.01 mA-50 mA.

What is claimed is:
 1. A method for determining the direction of apedicle breach during pilot hole formation, comprising the steps of:forming an access corridor to a pedicle in a patient; forming a pilothole in the pedicle by advancing an instrument into the pedicle;rotating the instrument about a longitudinal axis during the pilot holeformation while simultaneously applying a stimulation signal to theinstrument; and determining the direction of the breach by monitoringneuromuscular responses to successive stimulation signals during therotation of the instrument.
 2. The method of claim 1, wherein theinstrument is configured to transmit an electric stimulation to thepedicle from a neurophysiology monitoring system communicatively linkedto the instrument.
 3. The method of claim 2, wherein the neurophysiologymonitoring system detects the presence of the breach by determining astimulation threshold at which muscles innervated by a nerve adjacent tothe pedicle respond to the successive stimulation signals.
 4. The methodof claim 3, wherein the instrument comprises an electrode, wherein themethod comprises the additional step of: determining a position of theelectrode about the longitudinal axis when the stimulation threshold islowest to indicate the direction of the breach.
 5. The method of claim4, wherein the instrument is insulated to prevent shunting of thestimulation signal along the length of the instrument.
 6. The method ofclaim 5, wherein the instrument includes a first uninsulated portionforming the electrode.
 7. The method of claim 1, wherein the pilot holeextends between an outer surface of the pedicle and an interior locationwithin the pedicle.
 8. A method for determining directionality duringsurgery, comprising the steps of: forming an access corridor to apedicle target site in a patient; advancing an instrument into thepedicle; and rotating the instrument about a longitudinal axis andsimultaneously transmitting an electrical signal to a nerve adjacent thepedicle from a neurophysiology monitoring system communicatively linkedto the instrument to determine the direction of a breach detected in thepedicle during pilot hole formation.
 9. The method of claim 8, whereinthe neurophysiology monitoring system detects the breach by determininga threshold stimulation level at which muscles innervated by the nerverespond to the stimulation signal.
 10. The method of claim 9, whereinthe instrument comprises an electrode, wherein the method comprises theadditional step of: determining a position of the electrode about thelongitudinal axis when the stimulation threshold is lowest to indicatethe direction of the breach.
 11. The method of claim 10, wherein theinstrument is insulated to prevent shunting of the stimulation signalalong the length of the instrument.
 12. The method of claim 11, whereinthe instrument includes a first uninsulated portion forming theelectrode.
 13. A method for determining the direction of a pediclebreach during hole formation, comprising the steps of: rotating aninstrument about a longitudinal axis during formation of a pilot holewithin a pedicle while simultaneously applying a stimulation signal tothe instrument; and determining the direction of the breach bymonitoring neuromuscular responses to successive stimulation signalsduring the rotation of the instrument.
 14. The method of claim 13,wherein the instrument comprises a proximal end and a distal end, thedistal end terminating at a distal tip, the distal tip having anelectrode arranged along a single side of the distal tip.
 15. The methodof claim 14, wherein the instrument is configured to transmit anelectric stimulation to the pedicle from a neurophysiology monitoringsystem communicatively linked to the instrument.
 16. The method of claim15, wherein the neurophysiology monitoring system detects the presenceof the breach by determining a stimulation threshold at which musclesinnervated by a nerve adjacent to the pedicle respond to the successivestimulation signals.
 17. The method of claim 16, wherein the methodcomprises the additional step of: determining a position of theelectrode about the longitudinal axis when the stimulation threshold islowest to indicate the direction of the breach.
 18. The method of claim17, wherein the instrument is insulated to prevent shunting of thestimulation signal along the length of the instrument.
 19. The method ofclaim 18, wherein the instrument includes a first uninsulated portionforming the electrode.
 20. The method of claim 13, wherein the pilothole extends between an outer surface of the pedicle and an interiorlocation within the pedicle.